TRUE SHARP EDGE ORIFICES®

e-mail: sales@birdprecision.com • www.birdprecision.com

One Spruce Street, P.O. Box 540569 • Waltham, MA 02454-0569 USA • (800) 454-7369 • fax: (800) 370-6308

To produce True Sharp Edge Orifices®, all the variables thatmight influence the Cd Value (Coefficient of Discharge) mustbe controlled during production. This includes the orifice holelength, edges, surface finishes, roundness and the elimination

of all tool marks,burrs, ragged edgesand irregularities. Ifany one of theseareas is not perfectlymanaged, the orificeflow rates will varyfrom piece to piece,thereby making itimpossible to predictflow with any accu-racy. See Figure 1:Cd for 3 EdgeProfiles (Approx).

Figure 1 illustrates that changing the edge profile of a SharpEdge Orifice will result in large fluctuations in Cd values. ATrue Sharp Edge Orifice® has a Cd value of .60. Introducing achamfered edge can boost Cd to as much as .9 and introduc-ing a radius may result in Cds up to .98. This illustrates howsignificant small alterations in orifice edges can be.

Chamfers and radiuses are even more difficult profiles torepeat in production. Chamfering or radiusing the orifice edgeintroduces more variables than a simple sharp edge. In asense, you have added another set of edges and surfaces intothe equation. As a result, the .9 and .98 values will be hard tomaintain repeatedly. Sharp Edge Orifices with a Cd of .6 arepreferred by engineers because they are a simple profile andmore consistent if produced correctly.

Precision machine drilling of near perfect Sharp Edge Orificesis next to impossible. Drilling inherently can be a bruteprocess of cutting metal to generate a hole. Drills leave behindspiral tool marks, burrs, poor surface finish and out of roundor elliptical holes due to drill wobble. If the burrs are removedby chamfering then, as illustrated above, the Cd value isaltered. If they are not removed, then you have ragged edges.It is a catch 22. Secondary procedures, such as electro polish-

ing, while helpful, cannot remove all the irregularities that are created by the drilling process.

Because of the pitfalls of drilling, many manufacturers resort to individually flow checking each orifice. This can be labor intensive and expensive. The smaller the orifice, the more difficult it becomes to produce large quantities ofrepeatable orifices.

Keeping an orifice edge sharp after it is installed can be a critical issue, especially in high-pressure gas and liquid applications that can wear down the effective edge. If theinstrument has been calibrated, it may now significantlyundervalue the flow once the edge begins to radius from wearor damage

1. This is why orifices need to be made of hardened

and durable materials to reduce the wear factor. Making aTrue Sharp Edge Orifice® and keeping it is vital to maintain-ing flow settings of the instrument it is installed in.

True Sharp Edge Orifices® are successfully being produced economically by a non-traditional three-step process using acombination of laser drilling and wire lapping, in conjunctionwith surface lapping. Ruby is the material of choice since it is next to diamond in hardness, yet economical. This is a

man-made crystal grownfrom alumina powder, whichis melted at high temperatureto crystallize on a seed crystal to form a single crystal of either ruby (whichis red because of a chromium.05% dopant) or clear sapphire (no dopant) that isalmost chemically inert, 9mohs hardness (diamondbeing 10), with five times theabrasion resistance of carbide.Some applications in waterjet cutting approach 40,000psi using sapphire orifices.Where other materials, such

as hardened steel, would quickly erode away, the sapphirekeeps its edge under such extremes for a longer duration.

Figure 1. Source: Design Engineers Handbook,Parke Bulletin 0224-B1, Pg. g-9

Figure 2. Photo courtesy of BernardDubuis - Hrand Djevahirdjian SA - Industrie de Pierres Scientifiques -Monthey - Switzerland

PAUL A. BAILLIO, November 2003

TRUE SHARP EDGE ORIFICES®

e-mail: sales@birdprecision.com • www.birdprecision.com

One Spruce Street, P.O. Box 540569 • Waltham, MA 02454-0569 USA • (800) 454-7369 • fax: (800) 370-6308

Figure 2 illus-trates the rubyblanks being vibratory fed tothe laser forpiercing. This isthe best methodfor quickly get-ting throughthis hard mate-rial.

Figure 3 illustrates how the pierced ruby blanks are strungthousands at a time on long tapered wires. The wires are thenconnected to two large spools. The spools slowly advance thetaper in an oscillating motion through the strung rubies usingfine diamond slurry until the exact size orifice is achieved.The resulting holes are all identically round. Imparted fromthe roundness of the wire, they all will have a 2 micro inchpolished surface finish or better. Diameter tolerance within alot will vary less than .0001”, and overall tolerances of .0002”are the norm.

The final finishing operation is face lapping both sides of theorifice to bothcontrol the orifice throatlength, as wellas achieve thedesired sharpedges. The faceswill also have a 2 micro inchfinish. Theresult of thisthree-stepprocess is a True

Sharp Edge Orifice®. The Cd values will almost be identical,since all the variables that could influence them are controlled. The orifice edges will remain sharp longer in applications of high pressure, chemical or abrasive conditions.See Figure 4: .0100” Orifice 440X Power.

Thousands of cloned Sharp Edge Orifices are simultaneouslyand economically produced in sizes from .0016” and up. Theyare easily inserted into a variety of stainless brass or plasticfittings, connec-tors or inserts.

True Sharp EdgeOrifices® findapplication inanalytical instruments, gaschromatographs,gene splicingtools, medicalgas metering,chemical metering, sand blasting nozzles, critical flow restrictors forsampling instruments, pace makers, anesthesia orifices, nitrousoxide boosters, ink jet printers, leak detection masters, waterjet and various pneumatic regulator and hydraulic restrictor applications. See Figure 5: Finished Ruby Orifices.

Bird Precision of Waltham, Massachusetts produces True SharpEdge Orifices® exclusively by this three-step process andstocks over 140 unique sizes, along with an assortment ofstandard filtration and mounting options.

Bird Precision welcomes your visit to www.birdprecision.com,where you can learn more about these True Sharp EdgeOrifices®, or your call at 1-800-454-7369.

----------------------------------------------------------------1 For additional reading, see Operational Factors that Affect Orifice Meter

Accuracy, Flow Control Magazine, January 2003.

Figure 3.

Figure 4. .0100” Orifice 440X Power

Figure 5. Finished Ruby Orifices